/Engine/Source/Editor/UnrealEd/Public/WorkflowOrientedApp/WorkflowTabManager.h
Are we opening a new document, or restoring a previously opened document
enum EOpenDocumentCause { OpenNewDocument, ForceOpenNewDocument, RestorePreviousDocument, NavigatingCurrentDocument, QuickNavigateCurrentDocument, NavigateBackwards, NavigateForwards, NavigatingHistory, SpawnManagedDocument, CreateHistoryEvent, }